A barbarian has needs — a sword, a shield and roughly 56 chicken breasts a week. That’s what Jason Momoa ate while filming “Conan the Barbarian,” this summer’s big-screen reboot of the series that launched Arnold Schwarzenegger’s action movie career in 1982.

Over a few months in 2010, Momoa, a 6-foot-4-inch Hawaiian actor and model, added about 30 pounds of muscle to his 205-pound frame to play two high-profile, bare-chested plunderers — Conan and Khal Drogo, the 7-foot-tall warrior-king marauding on HBO’s “Game of Thrones.”

These massive men of summer are a shift from seasons past, when slight actors such as Tobey Maguire and Orlando Bloom populated the franchise movies and walking mountains like Johnson were encouraged to winnow their physiques to get parts. Some of this muscling up of summer’s heroes is driven by comic-book aesthetics and some, academics say, by cyclical notions of masculinity: In times when men are losing financial or societal power, biceps the circumference of tree trunks are proof of virility.

In addition to grueling workouts and meticulous nutrition, a number of celluloid hunks benefit from digital embellishments that make them appear even larger in marketing materials like posters and billboards. Many moviegoers may also wonder whether actors use steroids to build their bodies.

The actors interviewed for this story said they did not use illegal substances to pump themselves up. Yet some experts say the extreme images on screen, however achieved, may tempt men both in and outside of show business to consider using illicit products to keep up.